1. Field
This application relates generally to wireless communications, and more particularly to handling handovers during a wireless communication session.
2. Background
Enhanced Serving Cell Change (ESCC) is a feature in 3GPP Release 8 designed to improve reliability of the serving cell change procedure. In an ESCC procedure, the network receives a serving cell change request, such and an event 1d (e1d) measurement report message (MRM), and decides to perform a serving cell change. Rather than sending a Physical Channel Reconfiguration message on the source cell HSPDA link, the network sends HS-SCCH orders on the target cell to instruct the UE to start a serving cell change procedure.
Once a user equipment (UE) sends a change request message, the UE begins to monitor the HS-SCCH from the target cell. Once the network processes the change request, the network orders the target cell to send HS-SCCH orders. When a sufficient number of HS-SCCH orders are received by the UE, the UE sends an acknowledgement to the network and starts to receive data from the target cell.
In a rapidly changing RF environment, it is common to generate multiple measurement events back-to-back. In the ESCC procedure, as soon as an e1d MRM is sent, the UE starts to monitor the HS-SCCH for the target cell. That is, the UE assumes that the network will process the e1d MRM just sent by the UE next. However, the network is not required to process e1d MRM messages in the same order as is assumed by the UE. Accordingly, as only a single target cell is monitored at a time even where multiple e1d MRMs are pending, unnecessary serving cell change failure can occur if the e1d MRMs are not processing in the same order by the UE and the network. It would be desirable to have a system and method to alleviate these and other problems associated with the ESCC procedure.